Franklin County Public Health and Hilliard City Schools are investigating three potential cases of the mumps at Bradley High School, Brown Elementary School and J.W. Reason Elementary School.
One case was reported at each school, district spokeswoman Stacie Raterman said.
Mitzi Kline, communications director for Franklin County Public Health, confirmed May 12 the department is investigating three reports of mumps in Hilliard schools.
Two are students and one is an employee, Kline said.
"All three cases are probable cases that have not been confirmed," Kline said.
Still, all three individuals are not at their respective schools, Kline said.
Vicky Clark, director of student support services, advised district parents of the investigation May 12 via email and letters to parents.
The district recommended every child receive two doses of the MMR (measles, mumps and rubella) shot.
Two doses of the vaccine are about 88 percent effective.
At least one of the Hilliard cases involved a vaccinated student, Raterman said.
The district's email and letters also indicated unvaccinated students possibly could be required to stay out of school for at least 25 days after the onset of any symptoms associated with mumps.
About 1.5 percent of Ohio public-school students are not vaccinated, according to The Columbus Dispatch.
State law requires treating physicians and clinics to notify the board of health of any patients exhibiting symptoms of the mumps, Kline said, as was the case with the individuals at the three Hilliard schools.
As of May 12, the three probable cases would raise the number of probable and confirmed cases in central Ohio since Jan. 7 to 342, Kline said, all associated with the original outbreak tied to the Ohio State University.
Hilliard is the second school district in central Ohio to report mumps cases, according to The Dispatch.
In April, five Olentangy Local Schools students were forced to stay home for at least 25 days or until they received a mumps vaccine after a cluster of two cases was discovered in the district.
Dispatch staff writer Rick Rouan contributed to this story.